Today's PC is capable of displaying literally millions of shades of colors. However, when it comes to designing web sites, most web developers rely on what is called the 216 "web safe" colors.
Well, it's near impossible to assign a "name" to every one of 216 shades of colors, much less the millions of shades of colors. So, instead of names, we often use numbers. The numbers simply represent the mix of red, green and blue. In the example above, 00 represents the amount of red, CC the amount of green, and 66 the amount of blue.
Samantha from the CuteSITE Builder Discussion forum has put together some wonderful information describing the colors that can be used with CSB/Trellix Web.
And here are some links to other web sites with their own web color charts: